Type of Document	Dissertation
Author	Rogers, Sydana D.
URN	etd-08192004-103718
Title	Chromatographic Silanol Activity Tests: The Development of a Comprehensive Test Procedure
Degree	Doctor of Philosophy
Department	Chemistry and Biochemistry, Department of
Advisory Committee	Advisor Name Title John G. Dorsey Committee Chair Ernest L. McDuffie Committee Member Kenneth A. Goldsby Committee Member Thomas J. Vickers Committee Member
Keywords	Silanol Activity Chromatography
Date of Defense	2003-12-13
Availability	unrestricted
Abstract There is great interest in the analysis of stationary phases used in reversed-phase liquid chromatography, with a strong emphasis on the evaluation of residual silanols. A number of techniques have been developed in order to assess the level of silanol activity in reversed-phased columns; however, to date there is no universally accepted test procedure. The overall goal of this work was to develop such a test. The invention of a universally accepted test would allow for a classification system for reversed-phase columns that would enable researchers to select columns more appropriately. The project consisted of two phases. In phase I of this study, several different silanol activity tests were compared. Test procedures were performed on a large collection of columns, including some of the most popular C18 phases used for the analysis of basic solutes. Column rankings, ranging from a low silanol activity to a high silanol activity, were determined according to the specifications of each test. Column rankings varied significantly among tests, suggesting that the current chromatographic silanol activity tests are not all testing for the same property. A number of unresolved issues from the literature were also addressed in this study. It was revealed that the older test procedures were inept at distinguishing between newer generation phases. Newer test procedures were shown to be more in agreement with each other than older test procedures. Test procedures were examined as candidates for a comprehensive procedure; however, none of the current tests were found to include all of the necessary components. Results indicated the need for a new approach in the development of a universal test procedure. In Phase II of this study, an attempt has been made to develop a universally accepted chromatographic silanol activity test procedure. This procedure analyzed all of the major interactions which comprise the term ‘silanol activity’, namely hydrogen bonding and ionic interactions. Aromatic compounds with nitrogen groups were selected as test solutes. These compounds had pKa values between 4 and 11. The new procedure took into account the pKa shifts that occur upon the addition of organic modifier. This test analyzed the basic compounds at mobile phase pH values ranging from 2.5 to 7.5 by utilizing a single mobile phase system which can be used in a pH gradient. This approach allowed for the analysis of the columns performance at all possible pH ranges for nondestructive use of the column. Results from the isocratic portion of this procedure illustrated the ability of the procedure to predict silanol activity at different pH levels when compared to results from everyday analyses. This work further demonstrated the need for testing columns over their entire useful pH range. An attempt was made to shorten the procedure by using the mobile phase system to create a pH gradient. Although analysis times were decreased greatly, the ability of the test to predict a column’s performance according to silanol activity was also diminished. Overall, gradient experiments provided solid foundational investigations into a radically different approach to silanol activity assessment.
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